There are air conditioners that improve energy efficiency by detecting a person by a human detector and by controlling the air-conditioning of indoor air depending on whether there is a person in a room. As the air conditioners, there is an air conditioner having a function of diagnosing whether the operating state of the human detector is normal or abnormal. For example, Patent Literature 1 discloses an apparatus that diagnoses whether the operating state of the human detector is normal or abnormal on the basis of a voltage level that is input to a signal processing unit within the time set after a power supply voltage of the human detector enters an ON-state. Patent Literature 2 discloses an apparatus that includes a unit for forcibly generating a signal of the human detection sensor, and diagnoses whether the operating state of the human detector is normal or abnormal, by operating the unit for forcibly operating the signal of the human detection sensor to detect whether the signal is generated by the human detection sensor.